When a monitoring camera for capturing images of an object(s) outdoors performs image capturing during a snowfall, the object(s) to be monitored may be obscured by many snow particles and can be unclear in the images captured. Such noise appearing in the captured image due to snow particles (hereinafter referred to as snowfall noise) hinders the monitoring, and thus, should be removed from the captured images.
To meet such a demand, technology is proposed in which median processing in the time direction is performed on multiple temporally consecutive captured images to remove the snowfall noise (see Patent Document 1 and Non-Patent Document 1). This technology is based on the fact that the probability that a pixel at the same coordinate represents a snow particle in multiple temporally consecutive captured images is low, and by performing median processing in the time direction, in which pixel values extracted from multiple temporally consecutive captured images are rearranged in the order of magnitude to obtain a median value, it is possible to remove the pixel values representing snow particles, thereby removing the snowfall noise.